红楼梦 - 第一回: Chunk 15

The next part has a small difference between the online text and the printed copy I have. The online text has: 此亦静极怂级 and my book has: 此亦静极思动.  I will use the online text, as that is probably the version most of us are reading.

这石凡心已炽,那里听得进这话去,乃复苦求再四.二仙知不可强制,乃道:"此亦静极怂级*,无中生有之数也.既如此,我们便携你去受享受享,只是到不得意时,切莫后悔."

Translation:

This stones desires already ablaze, therein hearing these words, then resumed its miserable beseeching fourfold. The two masters knowing they could not compel [the stone], then sighed, saying:  This [stone should] be exceedingly calm, [we] will formulate a plan. In this way, we will take you to enjoy [the human world], only [if you] are not satisfied, be certain to have no regrets.

Breakdown:

这石凡心已炽 -> This stones desires already ablaze
(Or its heart aflame with desire etc.)

那里听得进这话去 ->  therein hearing these words
(This is a simple construction, but it is difficult to translate the exact meaning.)

乃复苦求再四 -> then resumed its miserable beseeching fourfold.
(复....再四 meaning to reduplicate some action a given number of times.)

二仙知不可强制,乃叹道: -> The two masters knowing they could not compel
[the stone], then sighed, saying:

此亦静极怂级,无中生有之数也 ->  This [stone should] be exceedingly calm, [we] will formulate a plan.
(Another difficult phrase, the lack of pronouns is confusing, so I just guessed the meaning.)

既如此,我们便携你去受享受享 -> In this way, we will take you to enjoy [the human world]
(既如此 could also mean: Thus; Since; Now that; ...)

只是到不得意时,切莫后悔 -> only [if you] are not satisfied, be certain to have no regrets
(Or perhaps: only if [the world] is not pleasing [to you]....)